A variety of foods such as meat, vegetables and poultry are commonly batter coated, breaded and then cooked by deep fat frying. In addition, many dough products such as pizza dough, scones, and other dough-based food products are fried in oil. Often many of these foods are partially cooked (e.g., par-fried or par-baked) and then frozen. The frozen products are subsequently sold to the food service industry or to consumers for finish cooking, either by baking or finish frying. During such cooking operations, considerable amounts of fat or oil are often absorbed by the food being cooked. The extent to which absorption can occur is illustrated by the fact that a typical oil fried pizza crust often contains about 9.5% oil, which is absorbed during the frying step.
Current research on the absorption of fat and oil into food products indicates that when a food product is removed from oil the condensation of steam produces a vacuum effect (see, e.g., Gamble, et al. (1987) J. Food Engineering 29:227-248). The amount of oil absorbed depends on the amount of water removed and how it is removed from the product after frying. According to Ufheil and Escher (Lebensmittel-Wissenschaft und Technologie 29:640-644, 1996), oil uptake is a surface phenomenon and that the counter-flows of water vapor and oil are related to each other (but are not necessarily synchronized). Similarly, a reduction in “interfacial tension” between the food and the frying oil causes excessive oil pick up by the fried food product.
Tests have shown that most of the oil during frying is confined to the surface area of the food being fried. Furthermore, most of the oil is absorbed during the cooling period after the food product has been fried in oil (see, e.g., Ufheil and Escher (1996) Lebensmittel-Wissenschaft und Technologie 29:640-644; Moreira, R. G., et al. (1997) J. Food Engineering 31:485-498; and Aguilera, J. M. and Gloria-Hernandez, H. (2000) J. Food Science 65:476-479). Some research suggests that the microstructure of the crust or surrounding exterior region of a food product may be the most important determinant of the final oil uptake into that particular food (see, e.g., Bouchon, P. and Pyle, D. L. (2004) J. Food Science: Food Engineering and Physical Properties, vol. 69, Nr. 3).
Recognition of the extent to which current cooking operations result in the absorption of fat and oil raises several concerns. For food processors, the concern is the extra cost associated with replacing fryer oil or fat lost during the cooking process. For consumers, high fat and oil content in food raises dietary and nutritional concerns.
In view of such concerns, various attempts have been made to either reduce oil and fat absorption during frying, or to remove absorbed oil or fat post frying. Strategies for draining excess oil from fried foods include, for example, passing the food over a screen and allowing oil to drain off and/or using high velocity streams of hot air to blow off excess oil. Pre-frying treatments, such as lowering the moisture content of food before frying using microwave, hot-air treatment and/or baking has also been tried as a means to reduce absorption of fat and oil. These approaches, however, often require additional equipment and are time consuming.
To reduce fat absorption, tapioca dextrins and high amylose starches have been applied to food to form insoluble films that hinder oil absorption. Starch based systems, however, can be sensitive to the mode by which the starch is applied and the particular starch utilized. Examples of starch-based coatings are discussed for example in U.S. Pat. Nos. 5,648,110 and 6,001,399. In a related approach, carbohydrates, such as alginates and celluloses, which are water soluble but relatively insoluble in fat and oil, have been applied to foods to reduce oil absorption during frying. But the success of this approach also can depend upon the particular carbohydrate utilized and the mode of application.
Some have suggested that certain proteins be included in coatings applied to foodstuffs to reduce fat or oil absorption, but cautioned against the use of other proteins. Examples of various approaches of this type are discussed in U.S. Pat. Nos. 4,935,251; 5,217,736; 5,527,549; and 6,288,179.
Because of the limitations associated with the foregoing approaches, there thus remains a need for methods that effectively reduce the absorption of fat and/or oil during cooking to accommodate the demands of an increasing number of health-conscious consumers for foods that are lower in fat and caloric content and the demands of food processors for less wasteful cooking methods.